Polymer sheet, method of installing and producing same

ABSTRACT

A polymer sheet adapted to attach to a material body such as a ceiling of a geological cavity and provide protective cover. The sheet comprises: a webbing portion defining a plurality of primary openings; and two margin portions extending along opposite edges of the sheet on either side of the webbing portion along a length of the sheet, each margin portion defining a plurality of secondary openings, wherein the margin portions are angled relative to the webbing portion.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.16/322,577, filed Aug. 2, 2017, which claims the benefit ofInternational Application No. PCT/AU2017/050811, filed Aug. 2, 2017,which claims priority to Australia Patent Application No. 2016903033,filed in Australia on Aug. 2, 2016, each of which is incorporated hereinby reference in its entirety.

TECHNICAL FIELD

The present disclosure generally relates to sheet products suitable forattachment to a material body. More specifically, the present disclosurerelates to polymer sheet products for providing protection from loosematerial falling from a material body and methods for producing andinstalling these products.

BACKGROUND

Underground mining operations involve the excavation of cavities such astunnels. When a mine cavity is dug out, the material ahead of the miningexcavator is removed and, while supporting the roof with anothermachine, 1.2-1.5 m deep holes may be drilled into the ceiling about 1 mapart. A long rock bolt packed with an expanding glue resin can beinserted into these holes. Once the long bolt is anchored in position, aplate and nut may be attached to the end of the long bolt to tension thelong bolt. This creates a compression load on the surrounding rock toreduce the risk of the ceiling or walls of the mine cavity collapsing.

Despite advances in automating mining technology, mining operators maystill need to work in such tunnels. One of the dangers faced by miningoperators or mine workers in an underground tunnel is from rocks orother debris that may fall from the ceiling of the mine cavity. It is arequirement in underground mining to mitigate or limit the falling ofdebris such as loose rock from the ceiling or wall. In particular, thereis a need to reduce the risk of injury from large rocks falling ontomining operators.

To reduce this risk, a metal mesh product comprising metal rods may besecured in place on a ceiling while the long rock bolts are installed. Aplate and nut attached to the long bolts may be used to secure the metalrod mesh in place on the ceiling of the mine cavity. Rocks that arelarger than the gaps in the metal mesh or rocks that are directlycontacting the metal rods of the metal mesh may be thereby restrictedfrom falling from the ceiling.

However, the mesh may have exposed ends of metal rods which can causeinjury to operators installing the mesh. The metal mesh may beundesirably heavy which makes it difficult to transport deep into themine and difficult for workers to install without the use of specialisedequipment or machinery. The metal mesh also has relatively large gapsbetween the metal rods compared to the width of the metal rods.Additionally, the conductive nature of metal and alkalinity of groundwater leads to corrosion which reduces the expected service life of themetal mesh product.

Any discussion of documents, acts, materials, devices, articles or thelike which has been included in the present specification is not to betaken as an admission that any or all of these matters form part of theprior art base or were common general knowledge in the field relevant tothe present disclosure as it existed before the priority date of eachclaim of this application.

SUMMARY

Some embodiments relate to a polymer sheet adapted to attach to amaterial body and limit loose material passing the polymer sheet, thesheet comprising:

a webbing portion defining a plurality of primary openings; and

two margin portions extending along opposite edges of the sheet oneither side of the webbing portion along a length of the sheet, eachmargin portion defining a plurality of secondary openings, wherein themargin portions are angled relative to the webbing portion.

Some embodiments relate to a polymer sheet adapted to attach to aceiling of a geological cavity and provide protective cover, the sheetcomprising:

a webbing portion defining a plurality of primary openings; and

two margin portions extending along opposite edges of the sheet oneither side of the webbing portion along a length of the sheet, eachmargin portion defining a plurality of secondary openings, wherein themargin portions are angled relative to the webbing portion.

In some embodiments, the sheet is shaped such that the margin portionsare angled out of a webbing plane defined by the webbing portion and thesheet defines elongate creases between the webbing portion and eachmargin portion. In some embodiments, the margin portions are angled outof the webbing plane in opposite directions on either side of thewebbing plane. In some embodiments, the elongate creases form an obtuseangle between the webbing portion and either of the margin portions inthe range of 140° to 160°.

In some embodiments, the plurality of primary openings are arranged in aregular array. In some embodiments, the secondary openings defined bythe two margin portions are arranged in a regular array. In someembodiments, the regular array of secondary openings in each marginportion is the same so that, when either one of the margin portions anda margin portion on an identical but separate sheet are overlapping, atleast two of the secondary openings are aligned.

In some embodiments, the separation between the secondary openings isgreater than the separation between primary openings.

In some embodiments, the sheet comprises a plurality of webbing portionsand adjacent webbing portions are separated by a wider web portionextending between the margin portions. In some embodiments, thedimension of the wide web portion is greater than the largest dimensionof the openings.

In some embodiments, the sheet is a self-supporting structure and isflexible.

In some embodiments, the polymer sheet comprises any one ofpolypropylene, polyethylene, low-density polyethylene, medium-densitypolyethylene, high-density polyethylene, polymers of olefins,Acrylonitrile butadiene styrene (ABS), polycarbonate and amorphouspolymers.

In some embodiments, the sheet has a thickness in the range of about 1mm to about 12 mm.

Some embodiments relate to a method of installing protective covering ona ceiling of a geological cavity comprising:

positioning a first polymer sheet according to any one of the precedingclaims near or on the ceiling;

attaching a first portion of the first polymer sheet to the ceiling,wherein the attaching comprises using fasteners to attach the firstportion to the ceiling, and a first section of each fastener is attachedto the ceiling while a second section of each fastener passes througheither a primary or secondary opening defined by the first polymersheet.

In some embodiments, the method further comprises attaching a secondportion of the first polymer sheet to the ceiling, the first portion isnear a first end of the first polymer sheet and the second portion isnear a second end opposite the first end along the length of the firstpolymer sheet.

In some embodiments, the method further comprises:

positioning a second polymer sheet according to any one of the disclosedembodiments such that: the second polymer sheet partially overlaps thefirst polymer sheet, and at least one of the primary or secondaryopenings in the second polymer sheet is aligned with a primary orsecondary opening in the first polymer sheet; and

attaching at least one portion of the second polymer sheet to theceiling.

In some embodiments, attaching the at least one portion of the secondpolymer sheet comprises using the same fasteners used to attach thefirst or second portion of the first polymer sheet to the ceiling, andthe second section of the fasteners pass through aligned openings in thefirst and second polymer sheet.

In some embodiments, the positioning comprises overlapping a firstmargin portion of the first polymer sheet and a second margin portion ofthe second polymer sheet.

In some embodiments, at least two portions of the second polymer sheetare attached to the ceiling and at least one portion is near a first endof the second polymer sheet and at least one portion is near a secondend opposite the first end along the length of the second polymer sheet.

Some embodiments relate to a method of producing a polymer sheet adaptedto attach to a ceiling of a geological cavity and provide protectivecover, the method comprising:

extruding a polymer material into a sheet with a length and a width;

forming a plurality of primary openings in a webbing portion and aplurality of secondary openings in each of a first and second marginportion, wherein the first and second margin portion extend alongopposite edges of the sheet on either side of the webbing portion alongthe length of the sheet;

shaping the sheet such that the first and second margin portion areangled relative to the webbing portion.

In some embodiments, forming the plurality of openings comprisesstamping the openings through the sheet. In some embodiments, theplurality of primary openings are formed in a regular array. In someembodiments, the one or more secondary openings are formed in a regulararray. In some embodiments, the regular array of secondary openings inthe first margin portion is produced to be the same as the regular arrayof secondary openings in the second margin portion so that, when eitherof the first or second margin portion and a margin portion on anidentical but separate sheet are overlapping, at least two of thesecondary openings are aligned.

In some embodiments, shaping the sheet comprises heating the sheet tosoften the sheet. In some embodiments, the sheet is shaped such that themargin portions are angled out of a webbing plane defined by the webbingportion and the sheet defines elongate creases between the webbingportion and each of the first and second margin portions. In someembodiments, the sheet is shaped such that the first margin portions isangled out of the webbing plane in a first direction and the secondmargin portion is angled out of the webbing plane in a second directionon the other side of the webbing plane.

In some embodiments, the separation between the secondary openings isgreater than the separation between primary openings.

In some embodiments, forming the plurality of primary openings resultsin a plurality of webbing portions, and adjacent webbing portions areseparated by a wider web portion extending between the margin portions.

In some embodiments, the polymer comprises any one of polypropylene,polyethylene, low-density polyethylene, medium-density polyethylene,high-density polyethylene, polymers of olefins, Acrylonitrile butadienestyrene (ABS), polycarbonate and amorphous polymers.

In some embodiments, the method of producing the polymer sheet furthercomprises cutting the sheet along the width to form a separate sheet andthe length of the sheet. Throughout this specification the word“comprise”, or variations such as “comprises” or “comprising”, will beunderstood to imply the inclusion of a stated element, integer or step,or group of elements, integers or steps, but not the exclusion of anyother element, integer or step, or group of elements, integers or steps.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments are described in further detail below, by way of example,with reference to the accompanying drawings briefly described below:

FIG. 1A is a top view of a polymer sheet according to an embodiment;

FIG. 1B is an isometric view of the polymer sheet shown in FIG. 1A;

FIG. 1C is an end on view of the polymer sheet shown in FIGS. 1A and 1B;

FIG. 2 is a perspective view of two adjacent and partially overlappingpolymer sheets according to an embodiment;

FIG. 3 is a perspective view of a polymer sheet according to anembodiment;

FIG. 4 is a perspective view of an apparatus for producing a polymersheet according to some embodiments;

FIG. 5 is a flow chart for producing a polymer sheet according to someembodiments;

FIG. 6 is a flow chart for installing polymer sheets on a ceilingaccording to some embodiments;

FIG. 7 is a perspective view of a punch tool according to someembodiments; and

FIG. 8 is a top view of the array of openings produced by the punch toolof FIG. 7 in a polymer sheet.

DETAILED DESCRIPTION

The present disclosure generally relates to sheet products suitable forattachment to a material body. More specifically, the present disclosurerelates to a polymer sheet product for providing protection from loosematerial falling from a material body and methods for producing andinstalling these products. For example, the material body may be ageological cavity or an embankment. The loose material may include rocksor other debris from the material body.

Referring to FIGS. 1A, 1B and 1C, a sheet 10 is illustrated according toan exemplary embodiment which is adapted to attach to a ceiling of ageological cavity or a surface of a material body and provide protectivecover. The geological cavity may be a mine cavity that is subterraneanand underground. This is intended to also include, for example a cavityor a tunnel within a mountain.

The sheet 10 is formed from a polymer material and comprises a webbingportion 20 defining a plurality of primary openings 22 extending throughthe webbing portion 20. The sheet 10 also comprises two margin portions30, 31 extending along opposite edges 12, 13 of the sheet 10 on eitherside of the webbing portion 20 along a length L of the sheet 10. The twomargin portions 30, 31 each define a plurality of secondary openings 32,33 extending through the margin portions 30, 31.

The sheet 10 is shaped such that the margin portions 30, 31 are angledrelative to the webbing portion 20. In some embodiments, the sheet 10 isshaped such that the margin portions 30, 31 are angled out of a webbingplane defined by the flat plane that the webbing portion 20 lies in. Thesheet 10 may therefore define elongate corners or creases 14, 15. Insome embodiments, the margin portions 30, 31 may be angled out of thewebbing plane in opposite directions on either side of the webbingplane.

An obtuse angle θ (FIG. 1C) may be defined between the webbing portion20 and each of the margin portions 30, 31. In some embodiments, theobtuse angle θ is in the range of 140° to 160°. In some embodiments, theobtuse angle θ is in the range of 145° to 155°. In some embodiments, theobtuse angle θ is about 150°.

Alternatively, the angle of the margin portions 30, 31 can be describedby an acute angle between the margin portion 30, 31 and the webbingplane, the acute angle being equal to the obtuse angle θ subtracted from180°.

Advantageously, the angled margin portions 30, 31 of the sheet 10 mayalso assist in increasing the rigidity of the sheet 10 such that thesheet 10 is less flexible in the direction along the length L of thesheet 10. This may assist in the attachment of the sheet 10 onto aceiling of a mining cavity as the entire sheet 10 can be supported andpressed up against the ceiling by supporting the sheet 10 at only one ortwo portions of the sheet 10. This may also assist in the maneuveringand transportation of the sheet 10 prior to installation.

Referring to FIG. 2 , the sheet 10 and an identical but separate sheet210 are positioned such that they are aligned along their lengths L andpartially overlapping. The angled margin portion 30 and a margin portion231 on the identical but separate sheet 210 may be overlapping. Thisconfiguration of sheets 10, 210 may advantageously slightly restrictrelative movement of the sheets 10, 210 in a direction along the widthsW of the sheets 10, 210. This configuration may also advantageouslyassist in keeping sheets 10, 210 in position while they are beingattached to a ceiling. and assist installation of adjoining sheets 10,210 in an array along the ceiling of a geological cavity. The firstmargin portion 30 may be positioned on top of the second margin portion231 and closer to the ceiling in an interlocking configuration. This mayadvantageously slightly restrict the sheets 10, 210 from moving apartfrom each other. Alternatively, the second margin portion 231 may be ontop of the first margin portion 30 in an abutting configuration. Thismay advantageously slightly restrict the sheets 10, 210 from movingcloser together and further overlapping each other. This may assist inaligning the sheets 10, 210 in the direction along the widths W during:installation, and storage of sheets 10, 210 if they are stacked on topof each other.

The at least one secondary opening 32 defined by margin portion 30 onsheet 10 is positioned such that, when the margin portion 30 and themargin portion 231 on the identical separate sheet 210 are overlapping,two or more secondary openings 33 on the separate sheet 210 are alignedwith at least two of the plurality of secondary openings 32 defined bythe margin portion 30 on sheet 10 when the sheets 10, 210 are aligned.The first margin portion 30 may be on top of the second margin portion231 and closer to the ceiling in an interlocking configuration.Alternatively, the second margin portion 231 may be on top of the firstmargin portion 30 in an abutting configuration. These configurationsadvantageously enable a fastener such as a rock bolt to be passedthrough one of the secondary openings 32 in sheet 10 and one of thesecondary openings 233 in sheet 210 to attach at least a portion of thesheets 10, 210 to the ceiling. Advantageously, this enables the sheets10, 210 to be simultaneously attached to the ceiling and to each other.This advantageously provides a secure attachment of sheets 10, 210 tothe ceiling to assist in retaining loose rocks that may be dislodgedfrom and otherwise fall from the ceiling. In an exemplary embodiment,the fastener may be attached to the ceiling of a mining cavity alongwith an associated plate.

The length L may be considered the distance along the longest edge ofthe sheet 10. In some embodiments, the sheet 10 has a length L in therange of 2 to 8 m or a length L in the range of 3 to 5 m. In anexemplary embodiment, the sheet has a longest length of about 4 m.

The width W of the sheet 10 may be measured as a top down projection ofthe 3-dimensional structure (see FIG. 2 ). In some embodiments, thewidth is in the range of 1 to 2 m. In an exemplary embodiment, the widthW is about 1.5 m.

The sheet may have a thickness defined as the dimension orthogonal toboth the length L and the width W. In some embodiments, the sheet has athickness in the range of 1 to 12 mm. In some embodiments, the sheet hasa thickness in the range of 4 to 8 mm. In an exemplary embodiment, thesheet has a thickness of about 6 mm. Advantageously, the thickness ofthe sheet 10 may be optimised to reduce the overall weight of the sheet10 while maintaining: rigidity in the sheet 10 to enable the sheet 10 tobe positioned on the ceiling while only being supported at one or twoportions; and/or strength to assist in capturing and/or retaining loosematerial that may be dislodged from the ceiling.

The margin portions 30, 31 may have a margin width W_(m) measured alongthe margin portion between the edges 12, 13 and the elongate creases 14,15. In some embodiments, the margin width W_(m) is in the range of 100to 200 mm.

In the exemplary embodiment shown in the drawings, the primary openings22 have a hexagonal shape. In other embodiments, the primary openings 22may have a circular shape, an elliptical shape or any other shape suchas a square, a rectangle or an octagon.

In the exemplary embodiment shown in the drawings, the secondaryopenings 32, 33 have a generally square shape with rounded corners. Insome embodiments, the secondary openings 32, 33 may have a circularshape, an elliptical shape or any other shape such as a square, arectangle or an octagon.

In some embodiments, the primary openings 22 are all the same shape andsize and/or the secondary openings 32, 33 in the margin portions 30, 31are all the same shape and size. In other embodiments, the primaryopenings 22 and secondary openings 32, 33 may be of different shapes andsizes.

In some embodiments, the primary openings 22 have a largest dimension inthe range of 50 to 110 mm. In some embodiments, the primary openings 22have a largest dimension in the range of 75 to 110 mm. In someembodiments, the primary openings 22 have a largest dimension of about100 mm. Advantageously, the primary openings 22 are dimensioned toreduce the overall weight of the sheet 10 while not being so large as toallow loose rocks that are large enough to pose an unacceptable dangerto mining operators to fall through the sheet 10.

In some embodiments, the primary openings 22 are arranged in a regularlyspaced array. In the exemplary embodiment illustrated, the array is aregular triangular array where the centres of each primary opening 22lies on the vertices of a triangular lattice which may give theappearance of a hexagonal array. In some embodiments, the webbingportion 20 is arranged to define each primary opening 22 at an equaldistance from each of its nearest primary openings 22. In someembodiments, the separation D1 between the edges 23 of each primaryopening 22 from the edge 24 of an adjacent primary opening 22 is in therange of 10 to 50 mm. In some embodiments, the separation D1 between theedges of the primary openings 22 is less than the largest dimension ofthe primary openings 22, optionally less than 50% or less than 30% ofthe largest dimension. The array may advantageously provide the webbingportion 20 with improved stress relief to distribute stresses within thewebbing portion and mitigate tearing or damage to the webbing portion20.

In some embodiments, the plurality of primary openings 22 are arrangedin a square array where the centres of the primary openings 22 lie onthe vertices of a square lattice. In these embodiments, the webbingportion 20 is arranged to define each primary opening 22 at an equaldistance from each of its four nearest primary openings 22.

In some embodiments, a plurality of secondary openings 32, 33 aredefined by the margin portions 30, 31 and the secondary openings 32, 33are arranged in an array. In the exemplary embodiment illustrated inFIGS. 1A, 1B and 1C, the array is a linear array. The secondary openings32 may be equally spaced from each other along the margin portion 30 andthe secondary openings 33 may be equally spaced from each other alongthe margin portion 31.

In some embodiments, the edges 36 of the secondary openings 32, 33 areseparated from the nearest edge 37 of an adjacent secondary opening 32,33 by a separation D2 in the range of 20 mm to 60 mm (FIG. 1A). In someembodiments, the separation D2 between the secondary openings 32, 33 isgreater than the separation D1 between primary openings 22. For example,the separation D2 between the edges 36, 37 of the secondary openings 32,33 may be greater than the separation D1 between the edges 23, 24 of theprimary openings 22, optionally more than 50% or more than 30% of theseparation D1. Advantageously, the larger separation D2 between theedges 36, 37 of the secondary openings 32, 33 provides additionalmaterial to the margin portion 30, 31 of sheet 10 to assist a fastenerto attach the sheet 10 to the ceiling of a geological cavity and toattach the sheet 10 to an adjacent and partially overlapping sheet 10,210. The additional material provided may also increase the strength ofthe margin portions 30, 31.

Referring to FIGS. 3 and 4 , in some embodiments the sheet 10, 310comprises a plurality of webbing portions 20, 320 where adjacent webbingportions 20, 320 are separated by an optional wider web portion 326extending between two margin portions 30, 31, 330, 331. In someembodiments, the width D3 of the wider web portion 326 is the shortestdistance between the primary openings 22, 322 from adjacent webbingportions 20, 320. The width D3 is greater than the separation D1 betweenprimary openings 22, 322 in the same webbing portion 20, 320. In someembodiments, the width D3 is in the range of 20 to 150 mm.Advantageously, the wider web portion 326 may increase the rigidity ofthe sheet 10, 310 in the direction along the width W of the sheet 10,310. This may assist mining operators when the sheet 10, 310 is beingattached to the ceiling of a mining cavity as the sheet 10, 310 may bepressed up against the ceiling by only supporting the sheet 10, 310 atone or two parts. The wider web portion 326 may also advantageouslyprovide additional support to retain loose rocks from the ceilingbecause they cover a larger area of the ceiling.

In preferred embodiments, the sheet 10 is formed from a polymermaterial. In some embodiments, the polymer material is selected from thegroup of: polypropylene, polyethylene, low-density polyethylene,medium-density polyethylene, high-density polyethylene, polymers ofolefins, Acrylonitrile butadiene styrene (ABS), polycarbonate andamorphous polymers. As polymer materials have a lower density thansteel, the sheet 10 may be advantageously lighter than a similarly sizedsteel mesh used to restrict loose material (such as rocks) from fallingfrom ceilings in mine cavities. Lighter weight sheets 10 areadvantageously easier to attach to a ceiling by mining operators as lesseffort is required to raise and support them against the ceiling.Furthermore, polymer materials are more resistant to damage fromcorrosion due to exposure to corrosive conditions such as exposure toacidic or alkaline substances.

In some embodiments, the sheet 10 may be formed from polymers comprisingadditives that increase electrical conductivity. This may advantageouslyreduce the risk of generating static charge which could cause sparks andstart dangerous fires or initiate deadly explosions.

In other embodiments, the additives can reduce conductivity of the sheet10. This may advantageously reduce the risk of electrical shock whencontacting the sheet 10, for example from a nearby lightning strike.

In some embodiments, the additives may act as a fire retardant and/orreduce the flammability of the sheet 10. In some embodiments, theadditives may enable the sheet 10 to be any one of luminous, fluorescentand phosphorescent.

In some embodiments, the webbing portion 20, 320 may be integrallyformed with the margin portions 30, 31, 330, 331.

In some embodiments the sheet 10, 310 may be flexible such that it isless likely to fracture or crack when flexed or deformed. The sheet 10may be elastically resilient such that it tends to retain its shape ifflexed or deformed.

An apparatus 400 for fabricating the sheet 10, 210, 310 is shown in FIG.4 . The apparatus 400 comprises an extruder 410 for extruding andproducing a continuous polymer sheet 412. The apparatus 400 furthercomprises an opening producing component 420 arranged to receive thecontinuous polymer sheet 412 and configured to produce primary openings22, 322 and secondary openings 32, 33 in the polymer sheet 412. In anexemplary embodiment, the opening producing component 420 may comprise ahole-punching apparatus comprising a punch tool. The opening producingcomponent 420 may be configured to repeatedly produce an array ofprimary openings 22 and secondary openings 32, 33. For example, theopening producing component 420 may repeatedly produce one or more linesof openings 22, 322, 32, 33 in the sheet 412 along the width W of thesheet 412 to progressively generate a longitudinally and laterallyextending array of primary openings 22, 322 and an array of secondaryopenings 32, 33 in the sheet 412.

FIG. 7 shows an exemplary punch tool 700 which, in some embodiments, maybe a part of the opening producing component 420. The punch tool 700 maybe mounted on an appropriate plate or substrate. When the sheet 412 isstationary, the punch tool 700 may be pressed against polymer sheet 412and pressed at least partially through the polymer sheet 412 toconcurrently produce lines of primary openings 22, 322 and secondaryopenings 32, 33 in the polymer sheet 412 in the corresponding array 800shown in FIG. 8 .

In some embodiments, the punch tool 700 may be formed from a tool steel.Tool steel generally has a greater hardness and/or wear resistancecompared to other iron alloys or carbon-steels and is therefore bettersuited for repetitively puncturing of the polymer sheet 412 to produceopenings 22, 322, 32, 33.

In some embodiments, the opening producing component 420 may beconfigured to produce secondary openings 32, 33 that are separated fromeach other by a distance D2 that is greater than the separation D1between the primary openings 22, 322 produced.

In some embodiments, the opening producing component 420 may beconfigured to produce a plurality of webbing portions 20, 320 thatdefine a plurality of primary openings 22 separated by a wider webportion 326 extending across the width of the sheet 310, 412.

Apparatus 400 also comprises a sheet forming component 430 for shapingthe sheet 412 to produce sheet 10, 310. The sheet forming component 430is arranged to receive the sheet 412 after primary and secondaryopenings 22, 322, 32, 33 have been produced in it. The sheet formingcomponent 430 shapes the sheet 412 to produce sheet 10, 310 where firstand second margin portions 30, 31, 330, 331 are angled out of a flatwebbing plane defined by the webbing portion 20, 320 and the sheet 10,310 defines elongate creases 14, 15 between the webbing portion 20, 320and each of the first margin portion 30, 330 and second margin portion31, 331.

In some embodiments, the sheet forming component 430 optionallycomprises a creasing component 432 to form two creases in the sheet 412to assist in shaping the sheet 412 and forming elongate creases 14, 15along the crease.

In some embodiments, the sheet forming component 430 comprises a formingheater 434 to heat the sheet 412. This advantageously softens the sheet412 to assist in shaping the sheet 412.

In some embodiments, the sheet forming component 430 comprises a set offorming rollers 436 to bend the sheet 412 along a line between thewebbing portion 20, 320 and the margins 30, 330, 31, 331 to thereby formthe elongate creases 14, 15. In embodiments that comprise a creasingcomponent 432, the forming rollers 436 are aligned such that the bend isformed along the crease to form elongate creases 14, 15.

In some embodiments, the apparatus 400 further comprises a cuttingcomponent 440 such as a guillotine to cut the sheet 412 along the widthW to form a separate sheet and limit the length L of the sheet 310.

In some embodiments, apparatus 400 comprises an injection mouldingcomponent for producing the polymer sheet 412. In some embodiments,apparatus 400 comprises a casting component for producing the polymersheet 412.

Methods of producing a sheet are described with respect to apparatus 400and/or punch tool 700 but the methods are not intended to be solelyrestricted to producing sheets with the specific apparatus 400 and/orpunch tool 700 shown and reference is only made to components ofapparatus 400 and/or punch tool 700 for illustrative and descriptivepurposes.

Referring to FIG. 5 , a method 500 of producing a sheet 10, 310 isprovided. The method 500 comprises extruding a polymer material, with anextruder 410, into a sheet 412 with a length L and a width W at 510. Themethod 500 further comprises forming, at 520, a plurality of primaryopenings 22 in a webbing portion 20, 320 and at least one secondaryopening 32, 33 in each of a first margin portion 30, 330 and secondmargin portion 31, 331 using the opening producing component 420. Thefirst and second margin portion 30, 330, 31, 331 extend along oppositeedges of the sheet 10, 310 on either side of the webbing portion 20, 320along the length L of the sheet 10, 310. The plurality of secondaryopenings 32, 332 are formed in each margin portion 30, 330, 31, 331 suchthat, when either margin portion 30, 31 and a margin portion 231 on theseparate sheet 210 that is identical to sheet 10, 310 overlap (see FIG.2 ), one or more secondary openings 233 on the separate sheet 210 arealigned with at least two of the plurality of secondary openings 32, 332defined by the margin portion 30, 330 on sheet 10, 310 when the sheets10, 210, 310 are aligned. The method 500 further comprises shaping witha sheet forming component 430, at 530, the sheet 10, 310 such that, thefirst or second margin portion 30, 31 are angled relative to the webbingportion 20.

In some embodiments, method 500 comprises injection moulding the polymermaterial, with an injection moulding component, into the sheet 412. Insome embodiments, method 500 comprises casting the polymer material,with a casting component, into the sheet 412.

In some embodiments, the forming 520 comprises stamping the primaryopenings 22, 322 and secondary openings 32, 33 through the sheet 412, at522. The stamping 522 may comprise using the punch tool 700 of theopening producing component 420 to produce the primary openings 22, 322and secondary openings 32, 33. The forming 520 may also compriseproducing a regular array of primary openings 22 and secondary openings32, 33, at 524. The forming 520 may also comprise producing secondaryopenings 32, 33 with a separation D2 between the secondary openings 32,33 that is greater than the separation D1 between the primary openings22 produced.

In some embodiments, the forming 520 comprises stamping or punching theprimary openings 22, 322 and secondary openings 32, 33 through the sheet412 with the punch tool 700. The sheet 412 may be flat at least in thesection being stamped or punched with openings 22, 322, 32, 33.

After a first set of at least one line of openings 22, 322, 32, 33 isproduced by the punch tool 700, the polymer sheet 412 may be advancedfor either a fixed time or distance so that another section of thepolymer sheet 412 that does not have any openings may underlie the punchtool 700 and thereby enable the punch tool 700 to be actuated to produceone or more lines of openings. The punch tool 700 may be controlled tomove in a periodic manner to produce an array of openings 22, 322, 32,33. In some embodiments, the opening producing component 420 may, forexample, be controlled to synchronise movement of the sheet 412 and themovement of the punch tool 700 to punch openings 22, 322, 32, 33.

In some embodiments, the forming 520 comprises producing a plurality ofwebbing portions 20, 320 comprising a plurality of primary openings 22that are separated by a wider web portion 326 extending along the widthW of the sheet 412.

In some embodiments, there may be a periodic delay in the movement ofthe punch tool 700 such that the wider web portion 326 results from theproduction of openings 22, 322, 32, 33. In some embodiments, the sheet412 may be periodically advanced for a greater time or a greaterdistance such that the wider web portion 326 results from the productionof openings 22, 322, 32, 33.

Optionally, the shaping 530 may comprise creasing the sheet 412 alongthe direction of its length L to assist bending of the sheet 412 toproduce elongate creases 14, 15, at 532. The shaping 530 may alsocomprise heating the sheet 412 to soften the sheet 412, at 534 prior toproducing creases 14, 15 (e.g. with forming rollers 436). In someembodiments, the sheet 412 is heated to around 150° C. The temperaturerequired to soften the sheet 412, however, depends on the polymermaterial it is formed from. When the sheet 412 cools down to a certaintemperature, which depends on the polymer material, the elongate creases14, 15 may be retained and sheet 412 may advantageously retain the newshape that has been formed.

In some embodiments, the shaping 530 comprises bending the sheet 412along a line between the webbing portion 20, 320 and the margins 30,330, 31, 331 to thereby form the elongate creases 14, 15, at 536. Forexample, the sheet 412 may be bent with forming rollers 436.

In some embodiments, the shaping 530 results in a sheet 10, 310 wherethe margin portions 30, 31, 330, 331 are angled out of a flat webbingplane defined by the webbing portion 20, 320. The shaping 530 may resultin a sheet 10, 310 where the first margin portion 30, 330 is angled outof the webbing plane in a first direction, and the second margin portion31, 331 is angled out of the webbing plane in a second direction on theother side of the webbing plane.

In some embodiments, the sheet 412 is extruded by the extruder 410 at arate of 0.5 to 2 m/min. In some embodiments, the sheet 412 is extrudedby the extruder 410 at a rate of 1.0 to 1.2 m/min. The extrusion rate isa function of the sheet width W, thickness and the material. Theextrusion rate is also dependent on the size of the extruder.

In some embodiments, the polymer material extruded in the extruding 510comprises any one of polypropylene, polyethylene, low-densitypolyethylene, medium-density polyethylene, high-density polyethylene,polymers of olefins, Acrylonitrile butadiene styrene (ABS),polycarbonate and amorphous polymers.

In some embodiments, the method 500 further comprises cutting the sheet412 using the cutting component 440 along the width W to form a separatesheet and limit the length L of the sheet 412, at 540.

Referring to FIG. 6 , a method 600 of installing a protective coveringon a ceiling of a geological cavity is disclosed. The method 600comprises positioning a first polymer sheet 10, 310 near or on theceiling, at 610. Then, at 620, attaching a first portion (not shown) ofthe first polymer sheet 10, 310 to the ceiling, wherein the attachingcomprises using fasteners (not shown) to attach the first portion to theceiling. A first section (not shown) of each fastener is attached to theceiling while a second section (not shown) of each fastener passesthrough either a primary opening 22 or a secondary opening 32, 33defined by the first polymer sheet 10, 310.

In some embodiments, the method 600 further comprises attaching a secondportion (not shown) of the first polymer sheet 10, 310 to the ceiling,at 622. The first portion (not shown) is near a first end (not shown) ofthe first polymer sheet 10, 310 and the second portion is near a secondend (not shown) opposite the first end along the length L of the firstpolymer sheet 10, 310. This may advantageously attach the entire sheet10, 310 to the ceiling.

The method 600 may also comprise positioning a second polymer sheet 210identical to the first polymer sheet 10, 310 such that: the secondpolymer sheet 210 partially overlaps the first polymer sheet 10, 310, at630. At least one of the primary openings 22 or secondary openings 32,33 in the second polymer sheet 210 is aligned with a primary opening 22or a secondary opening 32, 33 in the first polymer sheet 10, 310.

As an example, a stack of polymer sheets 10, 310 may be stored on top ofa vehicle (not shown) near the ceiling of the geological cavity. Apolymer sheet 10, 310 may be slid along its length L off the top of thestack and positioned onto the ceiling. The vehicle may repositionadjacent to the position where the second polymer sheet 210 is to bepositioned. The second polymer sheet 210 may then be slid along itslength L off the top of the stack and positioned onto the ceiling.

At least one portion of the second polymer sheet 210 may be attached tothe ceiling, at 632. Attaching 632 the at least one portion of thesecond polymer sheet 210 may also comprise using the same fasteners usedto attach the first or second portion of the first polymer sheet 10, 310to the ceiling, and the second section of the fasteners passes throughaligned openings in the first polymer sheet 10, 310 and second polymersheet 210. This advantageously attaches the first polymer sheet 10, 310and the second polymer sheet 210 to the ceiling.

In some embodiments, the positioning 630 of the second polymer sheet 210may comprise overlapping a first margin portion 30 of the first polymersheet 10, 310 and a second margin portion 231 of the second polymersheet 210. The first margin portion 30 may be on top of the secondmargin portion 231 and closer to the ceiling. Alternatively, the secondmargin portion 231 may be on top of the first margin portion 30. Usingthe same fastener to attach both sheets 10, 210, 310 along adjacent andoverlapping margin portions 30, 31, 231 of the two sheets 10, 210, 310reduces the total number of fasteners required, when compared to eachsheet 10, 210, 310 using separate fasteners.

In some embodiments, at least two portions of the second polymer sheet210 may be attached to the ceiling and at least one portion is near afirst end of the second polymer sheet 210 and at least one portion isnear a second end opposite the first end along the length L of thesecond polymer sheet 210. This may advantageously attach the entiresheet 10, 310 to the ceiling.

It will be appreciated by persons skilled in the art that numerousvariations and/or modifications may be made to the above-describedembodiments, without departing from the broad general scope of thepresent disclosure. The present embodiments are, therefore, to beconsidered in all respects as illustrative and not restrictive.

The invention claimed is:
 1. An extruded polymer sheet adapted to attachto a ceiling of a geological cavity and provide protective cover, theextruded polymer sheet comprising: a central webbing portion defining aplurality of primary openings and a flat webbing plane; and two marginportions extending along opposite edges of the extruded polymer sheet oneither side of the central webbing portion along a length of theextruded polymer sheet, each margin portion defining a plurality ofsecondary openings, wherein the primary openings and the secondaryopenings are arranged in lines across a width of the extruded polymersheet, the lines being repeated along the length of the extruded polymersheet to generate a longitudinally and laterally extending array, andwherein a separation between the secondary openings is greater than anadditional separation between the primary openings.
 2. An extrudedpolymer sheet adapted to attach to a ceiling of a geological cavity andprovide protective cover, the extruded polymer sheet comprising: acentral webbing portion defining a plurality of primary openings and aflat webbing plane; a first margin portion and a second margin portion,the first margin portion and the second margin portion respectivelyextending along opposite longitudinal edges of the extruded polymersheet on either side of the central webbing portion along a length ofthe extruded polymer sheet, each of the first margin portion and thesecond margin portion defining a respective plurality of secondaryopenings, wherein a separation between the secondary openings is greaterthan an additional separation between the primary openings; and a firstintermediate portion and a second intermediate portion, the firstintermediate portion extending between the first margin portion and thecentral webbing portion and the second intermediate portion extendingbetween the second margin portion and the central webbing portion. 3.The extruded polymer sheet of claim 2, wherein each of the firstintermediate portion and the second intermediate portion defines arespective elongate crease between the central webbing portion and arespective one of the first margin portion and the second marginportion.
 4. The extruded polymer sheet of claim 3, wherein eachrespective elongate crease is parallel to the longitudinal edges of theextruded polymer sheet.
 5. The extruded polymer sheet of claim 2,wherein each of the first intermediate portion and the secondintermediate portion is free of openings.
 6. The extruded polymer sheetof claim 2, wherein the primary openings have substantially a sameshape.
 7. The extruded polymer sheet of claim 2, wherein adjacent onesof the primary openings are approximately equally spaced apart from eachother.
 8. The extruded polymer sheet of claim 2, wherein the primaryopenings are arranged in a regular array.
 9. The extruded polymer sheetof claim 2, wherein the secondary openings have substantially a sameshape.
 10. The extruded polymer sheet of claim 2, wherein the secondaryopenings respectively defined by the first margin portion and the secondmargin portion are arranged in a respective regular array.
 11. Theextruded polymer sheet of claim 10, wherein the respective regular arrayof secondary openings in each margin portion is substantially the sameso that, when either the first margin portion or the second marginportion overlaps with an additional margin portion on an additional andseparate extruded polymer sheet, at least two of the secondary openingsare aligned.
 12. The extruded polymer sheet of claim 2, wherein thefirst margin portion and the second margin portion are parallel with theflat webbing plane.
 13. The extruded polymer sheet of claim 2, whereinthe extruded polymer sheet comprises a plurality of webbing portions,and wherein adjacent webbing portions are separated by an additional webportion extending between the first margin portion and the second marginportion.
 14. The extruded polymer sheet of claim 13, wherein theadditional web portion, the plurality of webbing portions, the firstmargin portion, and the second margin portion are parallel and/orcoplanar.
 15. The extruded polymer sheet of claim 13, wherein adimension of the additional web portion is greater than a largestdimension of the primary openings.
 16. The extruded polymer sheet ofclaim 2, wherein the primary openings have a first shape that isdifferent from a second shape of the secondary openings.
 17. Theextruded polymer sheet of claim 2, wherein the extruded polymer sheetcomprises any of polypropylene, polyethylene, low-density polyethylene,medium-density polyethylene, high-density polyethylene, polymers ofolefins, acrylonitrile butadiene styrene (ABS), polycarbonate, oramorphous polymers.
 18. The extruded polymer sheet of claim 2, whereinthe extruded polymer sheet has a thickness in a range of about 1 mm toabout 12 mm.
 19. The extruded polymer sheet of claim 2, wherein theextruded polymer sheet is a self-supporting structure and is flexible.20. A method of producing a polymer sheet adapted to attach to a ceilingof a geological cavity and provide protective cover, the methodcomprising: extruding a polymer material into a sheet with a length anda width; forming a plurality of primary openings in a webbing portionand a plurality of secondary openings in each of a first margin portionand a second margin portion, wherein the first margin portion and thesecond margin portion extend along opposite edges of the sheet on eitherside of the webbing portion along the length of the sheet, wherein theprimary openings and the secondary openings are arranged in linesrepeated along the length of the sheet to generate a longitudinally andlaterally extending array, wherein a separation between the secondaryopenings is greater than an additional separation between the primaryopenings; and shaping the sheet such that the first margin portion andthe second margin portion are parallel to the webbing portion.